A comparative study of sintered and melt-grown recrystallized YBa 2 Cu 3 O x
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Aaron Barkatt Department of Chemistry and Vitreous State Laboratory, The Catholic University of America, Washington, DC 20064
Arthur N. Thorpe and Matthew F. Ware Department of Physics, Howard University, Washington, DC 20059
Inna G. Talmy and Debbie A. Haught Naval Surface Warfare Center, Silver Spring, Maryland 20910
Sidney Alterescu National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, Maryland 20770 (Received 16 June 1988; accepted 4 October 1988) This paper compares the properties of yttrium barium cuprate bulk specimens prepared by means of solid-state sintering on one hand and of growth from a largely molten state on the other. The current paper focuses on magnetization measurements at 77 K which show specimens made by the latter method to have high remanence magnetization values.
I. INTRODUCTION It is generally recognized that among specimens of yttrium barium cuprate those which have high density and consist of large crystals of the pure orthorhombic phase can be expected to give the highest values of Jc and, correspondingly, sharp superconducting transitions in magnetic susceptibility. Unfortunately, since the oxygen-rich orthorhombic phase is metastable and exhibits incongruent melting, it has not proved possible to produce such samples directly by completely melting the material at high temperatures and growing crystals from the melt. Accordingly, in most studies specimens were prepared by a solid-state sintering process.1 The sintering process was systematically characterized, and it was found that grain size, sintering temperature, and sintering time were the most important factors involved in the production of highdensity sintered materials.2'3 However, a variety of methods, including flux,4 float zone,4'5 and nonstoichiometric partial melt growth4"8 and rapid solidification9 were investigated as potential techniques of inducing crystal growth. The preparative method used in the present study consisted of partial melting and crystallization, with the residual solid acting as seeds to induce crystallization of the orthorhombic phase. With certain variations detailed below, this technique is based on the approach used in the partial melt growth studies cited above, in particular Ref. 8. The main purpose of the present work was to characterize the magnetic properties (susceptibility and magnetization) of samples formed by grain growth following partial remelting, correlate them with chemical and structural measurements, and compare these samples with ones 28
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J. Mater. Res., Vol. 4, No. 1, Jan/Feb 1989
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prepared by solid-state measurements. The measurements were carried out at relatively high temperatures (around 77 K) in view of the importance of the high-temperature range in superconductor applications. II. PREPARATION Analytical grade dry Y2O3, BaCO3, and CuO powders corresponding to a stoichiometric Y: Ba: Cu ratio of 1:2:3 were mixed by ball-milling in acetone using zirconia grinding media. After drying, th
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